Field of the Invention
The invention relates to a roll and a method for manufacturing a roll for hot or cold rolling of flat metal products, wherein the roll has a barrel section which is coated with a wear-resistant layer and two journals oriented coaxially with the barrel section, one of which is in each case formed on one of the end faces of the barrel section.
Description of Related Art
Flat metal products which are cold or hot rolled using such rolls typically include strips, sheets or products cut from these which consist of steel or non-ferrous metal.
In practice, rolls used for flat metal products are, on the one hand, subjected to high dynamic forces as a result of the rolling forces occurring during rolling and are on the other hand subject to high wear in the region of their circumferential surfaces which come into contact with the rolled material.
In order to increase the service life of work rolls used for the hot rolling of hot steel strip, in DE 10 2009 037 278 A1 it has been suggested that a work roll which is used in a stand for the finish hot rolling of hot steel strip be provided with a wear-resistant layer consisting of powder-metallurgical material through hot isostatic pressing, also referred to in the technical jargon as “HIP”. A comparable suggestion can be found in EP 1 365 869 B1, according to which, in order to increase its resistance to wear, the work roll, also used for hot rolling, is provided with a layer applied using the HIP method.
During the manufacture of such work rolls, a main body consisting of cast iron or a suitable steel is first produced through casting or forging which comprises a barrel region which comes into contact with the rolled material in use and bearing journals via which the roll is mounted in the roll stand. The materials of the main body thereby exhibit mechanical properties which are optimally matched to the force loads which occur in practical use.
The main body prefabricated in this way is then encased in a sheet metal capsule. This is dimensioned such that a cavity surrounding the main body is formed between its inner circumferential surface and the circumferential surface of the barrel. This cavity is filled with an alloy powder. The sheet metal capsule is then sealed in a gas-tight manner. Compression then takes place under high pressure on all sides and at high temperature. The pressure and temperature are thereby adjusted such that the powder is compressed and sintered. In this way, a completely dense layer is formed on the main body in which the individual powder particles are sintered not only with each other but also with the main body, so that a homogeneous composite body is produced. Following the end of the hot isostatic pressing, the sheet metal capsule is removed. Finally, a thermal aftertreatment can take place in order to provide the obtained composite roll with the required mechanical properties. As a rule, a mechanical final processing also takes place in order to guarantee the required dimensional accuracy.
Modern roll trains are subject to increasingly demanding requirements in terms of the width of the rolled material which is to be processed. Accordingly, increasingly long rolls must be made available in order to allow greater widths to be rolled reliably. It proves problematic here that the coating of such long rolls using the HIP method involves considerable complexity. For example, the complexity of the equipment required for the hot isostatic pressing increases disproportionately with increasing length of the rolls. HIP plants which are currently available are therefore so limited in their length that they can no longer be used to process rolls the dimensions of which reflect the current requirements of roll train operators.
In order to solve this problem it has been suggested, in WO 2014/001024 A1, for the manufacture of rolls for cold or hot rolling of flat metal products, first to manufacture a main body which only extends over the barrel region of the roll which is to be manufactured, then to coat this main body with a wear-resistant layer through hot isostatic pressing and only then to weld to the main body the journals required in order to mount the roll rotatably in the roll stand. The fact that, according to this suggestion, the journals are only joined with the main body after the hot isostatic pressing means that the full length of the available HIP plants can be used for the HIP coating of the barrel region, whereas in a conventional approach not only the barrel region but also the journals formed onto the barrel region of the main body need to be accommodated in the HIP plant.